1. Field of the Invention
The present invention relates to a semiconductor laser and more particularly, to a II-VI semiconductor laser with burying layers for burying the heterostructure.
2. Description of the Prior Art
A conventional II-VI compound semiconductor laser of this sort is disclosed in Applied Physics Letters, Vol. 63, No. 17, pp2315-2317, October, 1993. This laser has a buried-ridge structure containing a CaAs substrate, MgZnSSe cladding layers, ZnSSe guiding layers, and a single strained, pseudomorohic CdZnSe quantum well, and a polycrystalline ZnS burying layers. The MqZnSSe upper cladding layer is selectively etched to form a ridge, and the ridge is buried by the ZnS burying layer.
However, in general, the heterostructure of the II-VI compound semiconductor materials has an energy band lineup termed the "type 2" or "staggered type". With the heterostructure of this type, which is made of first and second semiconductor layers, the first semiconductor layer has the bottom of the conduction band higher than that of the second semiconductor layer and the top of the valence band higher than that of the second semiconductor layer. Also, as the energy band gap increases, both of the bottom of the conduction band and the top of the valence band tend to come down.
As a result, if a semiconductor material having a large energy band gap is used for the burying layer, there is a problem that such the burying layer cannot confine electrons.